The present invention relates to packages and containers, preferably sterilizable containers used to house medical devices in a sterile environment. More specifically, the present invention relates to heat sealable, sterilizable polymeric bags including those having at least a portion of the bags comprising headers preferably made from a porous material to facilitate passage of a sterilizing agent. The present invention also relates to sterilizable plastic bags having headers made from polymeric film with such bags capable of being subjected to radiation sterilization.
Sterilizable containers in the form of pouches or bags are popular vehicles for storing and transporting sterile medical devices, including instruments, dressings, drapes, etc. Such pouches often utilize heat-sealed transparent plastic sheets, for example low density polyethylene, positioned face-to-face and sealed around the common periphery. Such packages often feature an access opening through which the contents of the package are removed, once the package is opened. Access openings are covered with a sealable strip commonly referred to as a xe2x80x9cheaderxe2x80x9d. The header may be made from a porous or non-porous material and is sealed to one or both of the plastic sheets to cover the access opening. The header is often made from a porous membrane and not only functions as a cover for the access opening, but also facilitates sterilizing the package contents. The porous characteristics of the membrane allow a sterilizing medium, such as sterilizing gas (e.g. ethylene oxide, etc.) or steam, to pass into and out of the pouch, while forming a sterile barrier against bacteria or other contaminants. The header also may be made from a nonporous material such as a polymeric film. Radiation sterilization may be used when the header is made from a nonporous material. Further, headers often serve as tear strips (or peelable strips commonly referred to as xe2x80x9ctear stripsxe2x80x9d herein) and allow a package user to remove the strip to gain access to the package through the access opening. When porous headers are desired, such porous membranes are most often made from a breathable medical grade paper or non-woven fabric, for example, medical grade Tyvek(copyright) (DuPont Company).
The way in which a header is sealed to a sterilizable package is often critical to the package""s success in the marketplace. For example, if the header is sealed too tightly to the package, header removal by peeling will be made more difficult or impossible. However, to properly sterilize the package, the header must be adhered securely to the package. The repeated sterilizing protocols required for the sterilizing medium to enter and leave the package under repeated vacuum and pressure, will cause the header to separate from the package if the header is not adhered securely enough. Therefore, much research has gone into arriving at the proper combination of header-to-bag seal strength versus header peelability.
Aseptic presentation is the introduction of the contents of a sterilized package into a sterile field without compromising the sterility of the contents of the field. Such presentation is often desirable and packages that permit delivery of contents in this way are also desirable. The release of any particulate matter from the header, upon opening, can compromise the sterile field, and is therefore unacceptable. Regardless of the coating used, it has been a problem for package designers to select the proper coating that both retains the desired porosity of the header to allow sterilizing agent entry at a desired rate, while also providing a good peelable seal between the header and the plastic sheet.
Another problem has been the breaking of the header bag end seal by the package contents as they are loaded into the bag. A package having a suitably strong top seal (at the header) is highly desirable. Additionally, package designers have compromised between peelable seals with a low enough strength to permit easy opening, and high seal strengths on the perimeter of the bag, primarily to end seal, insuring that the contents are retained during sterilization, shipping an handling.
Packages are known having the access opening located at a point away from the upper edge, or top, of the package. In this way, the package contents, upon package inversion, would only come in contact with a heat seal located away from the access opening. See U.S. Pat. No. 5,551,781. In such packages, the tear strip and interlayer between the tear strip and access opening are dimensioned to match the opening made in the upper plastic sheet. The interlayer is applied to the opening, and the porous material tear strip is then placed in contact with the interlayer. This design has many limitations including enhanced processing complexity and cost, as well as a restricted access opening area, as compared with a top opening design.
Other packages are known where the tear strip essentially covers the middle portion of the package which then opens outward. Once again, an interlayer is provided which adds to the overall complexity of the manufacturing process and therefore adds to overall cost. See U.S. Pat. No. 4,367,816.
Therefore, a sterilizable package having an enlarged access opening covered by a porous material that has its edge reinforced to prevent separation by package contents would be highly advantageous to the field of sterilizable packaging. Further, in terms of superior package design, it would be most desirable to have the access opening placed at the top of the package, such that once the header is peeled back or removed, the package could be easily opened and presented aseptically for sterile removal of the package contents.
According to the present invention, one preferred embodiment relates to a package comprising a first bottom sheet having a first length, and a second top sheet having a second length shorter than the first bottom sheet. The two sheets are placed in registration along their common lower or bottom edge. The two side edges are heat sealed. The bottom edge is left open for contents insertion. The upper edge is comprised only of the longer, lower sheet. The distance from the top edge of the top sheet to the top edge of the bottom sheet represents the dimension of the access opening. This opening is covered by a header made from a porous or nonporous material and acting as a peelable or tear strip which is heat sealed to the top sheet along its top edge and heat sealed to the bottom sheet along its top and side edges.
A tape or film strip having an adhesive on one side and a polymeric (e.g. plastic) backing on its other side is attached to the header along at least one edge, preferably its top edge, although more than one edge may have a tape applied thereto. The adhesive side is placed against the header material and adhered thereto. The header material with adhesive film in place is then placed against the plastic sheets for heat sealing. At the time of heat sealing, the polymeric back of the adhesive film at the top of the header material is heat sealed to the top edge of the lower or bottom polymeric sheet of the package. In this way, a strong polymeric material-to-polymeric material bond, such as a weld seal, is effected along the upper edge of the finished sterilizable container such that upon inversion or loading, any contents, even such contents having significant weight, will not separate the polymeric material-to-polymeric material seal. To further assist in making certain that contents only contact the polymeric material-to-polymeric material seal, an excess of tape preferably is adhered to the header. In this way the contents will not contact the header-to-tape seal. A more complete understanding of the invention can be had by reference to the following detailed description and the attached drawings.